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Astron. Astrophys. 333, 767-778 (1998)

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Detection of shear due to weak lensing by large-scale structure

P. Schneider 1, L. van Waerbeke 1, 4, *, Y. Mellier 2, 3, B. Jain 1, **, S. Seitz 1, *** and B. Fort 3

1 Max-Planck-Institut für Astrophysik, Postfach 1523, D-85740 Garching, Germany
2 Institut d'Astrophysique de Paris, 98 bis boulevard Arago, F-75014 Paris, France
3 DEMIRM, Observatoire de Paris, 61 Avenue de l'Observatoire, F-75014 Paris, France
4 Observatoire Midi-Pyrénées, 14 Avenue Edouard Belin, F-31400 Toulouse, France

Received 29 May 1997 / Accepted 21 January 1998


We present evidence for a coherent shear signal in a field containing the [FORMULA] radio-source PKS1508-05. Since there were no intervening mass concentrations known before targeting this field, we interpret this signal as due to weak lensing by large-scale structure. This result is the outcome of a re-analysis of the observations of Fort et al. (1996) in the fields of three high redshift QSO/radio-sources. Several tests of the robustness of the signal were performed: subdivision of the field and tests using simulated data with randomized ellipticity orientation; using the pixel-to-pixel autocorrelation function method to measure the shear; using the correlation function of the galaxy ellipticities with bootstrap resampling to estimate errors and to find the typical angular separation that dominates the signal. We find that the field of PKS1508-05 contains a robust shear signal of about [FORMULA] that is coherent over the [FORMULA] by [FORMULA] field. The signal is detected at a high level of significance ([FORMULA]) using the tests described above. Combining the three QSO fields, we find an rms shear of about [FORMULA] on the scale of a [FORMULA] field, however with a large uncertainty which is dominated by cosmic variance. This value is close to that expected from the cosmological mass distribution on that scale.

Key words: cosmology: observations – gravitational lensing – dark matter – large-scale structure of universe – methods: statistical

*Present address: Canadian Institute for Theoretical Astrophysics
**Present address: Johns Hopkins University
***Present address: Universitätssternwarte München

Send offprint requests to: P. Schneider

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© European Southern Observatory (ESO) 1998

Online publication: April 28, 1998